In hybrid vehicles, switchable clutches are used for example for the connection of an electric motor or for the separation of an internal combustion engine. To be able to switch the torques that prevail in a motor vehicle, use is made of hydraulically switchable clutches. The required hydraulic pressure is generated by a motor-pump unit and is fed to the cylinder-piston system via lines.
In the case of a hydraulic system, it is a basic disadvantage that there are high demands on the leak-tightness of the system. A further disadvantage is the outlay for filling during assembly, the measures for ventilation, the recycling of the hydraulic medium, the high temperature dependency of the viscosity, and the compressibility of the hydraulic fluid. The hydraulic working principle results in delivery flow and pressure pulsations in the case of hydrostatic positive displacement pumps being used, and also in operating noise (liquid-borne noise, body-borne noise), and high demands are placed on oil quality and filtration over the entire service life.
Electromagnetic actuators in the motor vehicle are operated using the 12-volt on-board electrical system. In the case of single-disk dry clutch embodiments, these normally serve for the connection of auxiliary assemblies and/or for the switching of multi-stage auxiliary assembly drives, for example the switching of a multi-stage compressor. Owing to the 12-volt on-board electrical system voltage, such clutches can only generate limited electromagnetic forces, and the transmissible clutch torques are correspondingly limited.
A hybrid module of a hybrid drive of a motor vehicle with an electric motor and a separating clutch is described in DE 10 2008 052 254 A1. The clutch is hydraulically actuated.
DE 10 2008 040 499 A1 presents a controllable separating clutch in a hybrid drivetrain of a motor vehicle. An input shaft and an output shaft lie in an axis, and the rotor of the electric motor is situated around the structural space of the spring-loaded clutch, which is hydraulically actuated.
An electric actuator for a device to be controlled is presented in DE 10 2005 018 259 A1. A drive and a transmission gearing act on a device; in the event of failure of the electrical supply, the clutch element opens.
Electromagnetic switching clutches are also known from DE 351 527 C and from DE 10 324 487 B4. JP 2010 274881 A presents an electromotive drive with input and output shafts and with two electrically switchable clutches integrated in the housing.
WO 2012/048842 A1 has disclosed a positively engaging clutch arrangement in which a stroke magnet effects an engagement of the clutch parts by way of an armature that can be pulled in. A spring element is arranged between the armature and one axially movable clutch part.